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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/fernet.rst | 2 | ||||
| -rw-r--r-- | docs/hazmat/primitives/asymmetric/ec.rst | 91 | ||||
| -rw-r--r-- | docs/hazmat/primitives/symmetric-encryption.rst | 23 | ||||
| -rw-r--r-- | docs/spelling_wordlist.txt | 2 |
4 files changed, 72 insertions, 46 deletions
diff --git a/docs/fernet.rst b/docs/fernet.rst index 1c4918ad..4b713a54 100644 --- a/docs/fernet.rst +++ b/docs/fernet.rst @@ -83,7 +83,7 @@ Specifically it uses: * :class:`~cryptography.hazmat.primitives.ciphers.algorithms.AES` in :class:`~cryptography.hazmat.primitives.ciphers.modes.CBC` mode with a 128-bit key for encryption; using - :class:`~cryptography.hazmat.primitives.ciphers.PKCS7` padding. + :class:`~cryptography.hazmat.primitives.padding.PKCS7` padding. * :class:`~cryptography.hazmat.primitives.hmac.HMAC` using :class:`~cryptography.hazmat.primitives.hashes.SHA256` for authentication. * Initialization vectors are generated using ``os.urandom()``. diff --git a/docs/hazmat/primitives/asymmetric/ec.rst b/docs/hazmat/primitives/asymmetric/ec.rst index 4b3c460e..0e19bb2e 100644 --- a/docs/hazmat/primitives/asymmetric/ec.rst +++ b/docs/hazmat/primitives/asymmetric/ec.rst @@ -1,6 +1,6 @@ .. hazmat:: -Elliptic Curve Cryptography +Elliptic curve cryptography =========================== .. currentmodule:: cryptography.hazmat.primitives.asymmetric.ec @@ -13,7 +13,7 @@ Elliptic Curve Cryptography Generate a new private key on ``curve`` for use with ``backend``. :param backend: A - :class:`~cryptography.hazmat.primtives.interfaces.EllipticCurve` + :class:`~cryptography.hazmat.primitives.interfaces.EllipticCurve` provider. :param backend: A @@ -21,10 +21,38 @@ Elliptic Curve Cryptography provider. :returns: A new instance of a - :class:`~cryptography.hazmat.primtivies.interfaces.EllipticCurvePrivateKey` + :class:`~cryptography.hazmat.primitives.interfaces.EllipticCurvePrivateKey` provider. +Elliptic Curve Signature Algorithms +----------------------------------- + +.. class:: ECDSA(algorithm) + + .. versionadded:: 0.5 + + The ECDSA signature algorithm first standardized in NIST publication + `FIPS 186-3`_, and later in `FIPS 186-4`_. + + :param algorithm: An instance of a + :class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm` + provider. + + .. doctest:: + + >>> from cryptography.hazmat.backends import default_backend + >>> from cryptography.hazmat.primitives import hashes + >>> from cryptography.hazmat.primitives.asymmetric import ec + >>> private_key = ec.generate_private_key( + ... ec.SECP384R1(), default_backend() + ... ) + >>> signer = private_key.signer(ec.ECDSA(hashes.SHA256())) + >>> signer.update(b"this is some data I'd like") + >>> signer.update(b" to sign") + >>> signature = signer.finalize() + + .. class:: EllipticCurvePrivateNumbers(private_value, public_numbers) .. versionadded:: 0.5 @@ -33,7 +61,7 @@ Elliptic Curve Cryptography .. attribute:: public_numbers - :type: :class:`~cryptography.hazmat.primitives.ec.EllipticCurvePublicNumbers` + :type: :class:`~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicNumbers` The :class:`EllipticCurvePublicNumbers` which makes up the EC public key associated with this EC private key. @@ -54,7 +82,7 @@ Elliptic Curve Cryptography provider. :returns: A new instance of a - :class:`~cryptography.hazmat.primtivies.interfaces.EllipticCurvePrivateKey` + :class:`~cryptography.hazmat.primitives.interfaces.EllipticCurvePrivateKey` provider. @@ -92,48 +120,35 @@ Elliptic Curve Cryptography provider. :returns: A new instance of a - :class:`~cryptography.hazmat.primtivies.interfaces.EllipticCurvePublicKey` + :class:`~cryptography.hazmat.primitives.interfaces.EllipticCurvePublicKey` provider. +Elliptic Curves +--------------- -Elliptic Curve Signature Algorithms ------------------------------------ - -.. class:: ECDSA(algorithm) - - .. versionadded:: 0.5 - - The ECDSA signature algorithm first standardized in NIST publication - `FIPS 186-3`_, and later in `FIPS 186-4`_. +Elliptic curves provide equivalent security at much smaller key sizes than +asymmetric cryptography systems such as RSA or DSA. For some operations they +can also provide higher performance at every security level. According to NIST +they can have as much as a `64x lower computational cost than DH`_. - :param algorithm: An instance of a - :class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm` - provider. +.. note:: + Curves with a size of `less than 224 bits`_ should not be used. You should + strongly consider using curves of at least 224 bits. - .. doctest:: +Generally the NIST prime field ("P") curves are significantly faster than the +other types suggested by NIST at both signing and verifying with ECDSA. - >>> from cryptography.hazmat.backends import default_backend - >>> from cryptography.hazmat.primitives import hashes - >>> from cryptography.hazmat.primitives.asymmetric import ec - >>> private_key = ec.generate_private_key( - ... ec.SECP384R1(), default_backend() - ... ) - >>> signer = private_key.signer(ec.ECDSA(hashes.SHA256())) - >>> signer.update(b"this is some data I'd like") - >>> signer.update(b" to sign") - >>> signature = signer.finalize() +Prime fields also `minimize the number of security concerns for elliptic-curve +cryptography`_. However there is `some concern`_ that both the prime field and +binary field ("B") NIST curves may have been weakened during their generation. -Elliptic Curves ---------------- +Currently `cryptography` only supports NIST curves, none of which are +considered "safe" by the `SafeCurves`_ project run by Daniel J. Bernstein and +Tanja Lange. All named curves are providers of :class:`~cryptography.hazmat.primtives.interfaces.EllipticCurve`. -There is `some concern`_ that the non-Koblitz NIST curves (identified by names -that start with "B" or "P") may have been intentionally weakened by their -generation process. - - .. class:: SECT571K1 .. versionadded:: 0.5 @@ -243,3 +258,7 @@ generation process. .. _`FIPS 186-3`: http://csrc.nist.gov/publications/fips/fips186-3/fips_186-3.pdf .. _`FIPS 186-4`: http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-4.pdf .. _`some concern`: https://crypto.stackexchange.com/questions/10263/should-we-trust-the-nist-recommended-ecc-parameters +.. _`less than 224 bits`: http://www.ecrypt.eu.org/documents/D.SPA.20.pdf +.. _`64x lower computational cost than DH`: http://www.nsa.gov/business/programs/elliptic_curve.shtml +.. _`minimize the number of security concerns for elliptic-curve cryptography`: http://cr.yp.to/ecdh/curve25519-20060209.pdf +.. _`SafeCurves`: http://safecurves.cr.yp.to/ diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst index abc2b076..586285b7 100644 --- a/docs/hazmat/primitives/symmetric-encryption.rst +++ b/docs/hazmat/primitives/symmetric-encryption.rst @@ -288,7 +288,7 @@ Modes Must be the same number of bytes as the ``block_size`` of the cipher. Do not reuse an ``initialization_vector`` with a given ``key``. -.. class:: GCM(initialization_vector, tag=None) +.. class:: GCM(initialization_vector, tag=None, min_tag_length=16) .. danger:: @@ -318,13 +318,23 @@ Modes You can shorten a tag by truncating it to the desired length but this is **not recommended** as it lowers the security margins of the authentication (`NIST SP-800-38D`_ recommends 96-bits or greater). - If you must shorten the tag the minimum allowed length is 4 bytes - (32-bits). Applications **must** verify the tag is the expected length - to guarantee the expected security margin. + Applications wishing to allow truncation must pass the + ``min_tag_length`` parameter. + + .. versionchanged:: 0.5 + + The ``min_tag_length`` parameter was added in ``0.5``, previously + truncation down to ``4`` bytes was always allowed. :param bytes tag: The tag bytes to verify during decryption. When encrypting this must be ``None``. + :param bytes min_tag_length: The minimum length ``tag`` must be. By default + this is ``16``, meaning tag truncation is not allowed. Allowing tag + truncation is strongly discouraged for most applications. + + :raises ValueError: This is raised if ``len(tag) < min_tag_length``. + .. testcode:: import os @@ -356,11 +366,6 @@ Modes return (iv, ciphertext, encryptor.tag) def decrypt(key, associated_data, iv, ciphertext, tag): - if len(tag) != 16: - raise ValueError( - "tag must be 16 bytes -- truncation not supported" - ) - # Construct a Cipher object, with the key, iv, and additionally the # GCM tag used for authenticating the message. decryptor = Cipher( diff --git a/docs/spelling_wordlist.txt b/docs/spelling_wordlist.txt index dc123493..d90547a8 100644 --- a/docs/spelling_wordlist.txt +++ b/docs/spelling_wordlist.txt @@ -29,6 +29,7 @@ introspectability invariants iOS Koblitz +Lange metadata namespace namespaces @@ -39,6 +40,7 @@ preprocessors pseudorandom Schneier scrypt +Tanja testability Ubuntu unencrypted |